Government regulations have placed ever increasing restrictions on the amounts and types of organic volatiles permitted to escape into the atmosphere from coatings compositions. Considerable efforts have been expended to develop coatings compositions that have a minimal amount of volatile organic components; and this had led to development of powder coatings, radiation-curable coatings, water-borne coatings, and high solid coatings. In these recent developments, the amounts of organic solvents present are minimal; consequently, there is little or no atmospheric pollution.
In the field of solvent coatings, efforts have been made to reduce the amount of volatile solvent present and to increase the amount of reactive components that will react to produce the coatings on the substrate. At a sufficiently high concentration of such components, one has what is known as a high solids coating composition. These are compositions that are applied in liquid form and dry to acceptable films without the evaporation of substantial quantities of solvents. Such compositions are described, for example, in U.S. Pat. Nos. 4,086,293 and 4,119,593. U.S. Pat. No. 4,086,293 describes compositions of a polyepoxide, a stannous salt and the reaction product of polycaprolactone polyol with an intramolecular carboxylic acid anhydride; U.S. Pat. No. 4,119,593 describes compositions of a polyepoxide, a stannous salt and a monocarboxylic acid compound. At column 5, lines 4 to 13 of U.S. Pat. No. 4,086,293, it is also taught that a portion of the hydroxyl groups of the polycaprolactone polyol can be initially reacted with an isocyanate and then the resulting product is subsequently reacted with the intramolecular anhydride; Example 4 shows the use of uranyl nitrate catalyst.
The major factors which have led to the development of high solids coatings, i.e., the deleterious effects of organic solvent in the atmosphere and the high cost of energy needed to drive off the solvent, have become even more pronounced. Consequently there is a continuing need for high solids compositions which require less energy to cure and result in less air pollution than heretofore known high solids compositions. One principle way to accomplishing these ends is to increase the solids content of the compositions. Therefore a high solids composition having higher solids than the compositions heretofore available, which is easily applicable to a substrate and which cures to a good satisfactory dry film would be of great importance.